1. Field
One embodiment of the present invention relates to a magnetic disk drive apparatus such as a hard disk drive and a method of controlling the magnetic disk drive.
2. Description of the Related Art
Recently, a hard disk drive has become an information recording medium having large capacity with a high reliability and has been widespread in various fields as, for example, a medium for recording computer data, image data, audio data and the like. In addition, a hard disk has been so downsized as to be built in a potable electronic device.
For this reason, in a current downsizing-oriented magnetic disk drive using a hard disk, a speed of writing and reading information is made higher, a drive count of the hard disk, i.e. a write count of information in the hard disk and a read count of information therefrom are reduced, and the battery power is thereby saved, by using a nonvolatile memory capable of writing and reading information at a high speed as a cache memory.
In other words, this kind of magnetic disk drive urges a nonvolatile memory to write information to the outside and read information therefrom, and urges the hard disk to transfer information to the nonvolatile memory, thereby accelerating writing and reading operations of information as seen from the outside and reducing the drive count of the hard disk. This magnetic disk drive, also referred to as a NV (nonvolatile)-cache applicable HDD (hard disk drive), has been proposed (Non Volatile Cache Command Proposal for ATA 8—ACS Revision 5).
As described above, in the HDD including the nonvolatile memory as cache, resistance to shock caused by vibration and drop can be increased as the drive count of the hard disk can be reduced. However, when the memory usage rate (amount) of the nonvolatile memory is beyond a certain threshold value, the hard disk needs to be driven to flush the data stored in the nonvolatile memory and write data to the hard disk (disk medium). At this time, when a shock is given to the HDD, the head may collide with the disk medium.